This invention relates to heat dissipation in a housing containing electronic circuitry, and more particularly, to an improved heat sink arrangement used with printed circuit boards mounted in close proximity to each other in an enclosed housing. It also applies to boards similarly arranged in an open air environment.
In co-pending U.S. patent application Ser. No. 08/531,467, there is described a non-imaging monitoring system which is useful, for example, in a highway traffic monitoring system. It is a feature of this system that the sensor and processing electronics are self contained in a single housing which is, for example, mounted in a relatively inaccessible location above a roadway. In co-pending U.S. patent application Ser. No. 08/965,942 there is described mounting apparatus by which a camera, printed circuit boards on which the processing electronics are installed, and ancillary components are conveniently installed in the housing, and done so in such a way as to make it easy to access and service the instrument. Because of the compactness of this equipment, the current module is approximately 18".times.6".times.7" in size, and a new module will be approximately 5".times.5".times.16", and the fact the electronics can be powered for substantial lengths of time, it is important that the heat generated by the equipment be readily and efficiently drawn away from the operating electronics and dispersed to the atmosphere. These systems are based on the use of PC/104 and PC/104-Plus form-factor, printed circuit boards assembled into a stack configuration. In this arrangement the spacing between adjacent PC boards is 0.6 inches, much less than that between components on adjacent boards. This short distance precludes the use of conventional heat sinks mounted atop the components to facilitate heat transfer away from the components. Since the enclosures are required to be sealed against the environment, forced air cooling is also precluded. Hence existing approaches to heat transfer design are inadequate for this purpose. With the approximately 40-50 watts of power consumed by the camera and processing electronics, heat build up within the housing is so great that the protective circuitry responsive to shut off the electronics in the event of a heat overload, typically will cause a shut down after only two hours of operation. It is therefore important, in order to provide equipment which can operate over prolonged periods of time, that a new heat transfer system be devised which will overcome these operational problems. This is especially important as electronic circuit density and clock speed get higher and higher.